Method and apparatus for testing a semiconductor device

ABSTRACT

Provided is an apparatus for testing a semiconductor device. The apparatus includes a plurality of testing pads. The apparatus includes a plurality of testing units. The apparatus includes a switching circuit coupled between the testing pads and the testing units. The switching circuit contains a plurality of switching devices. The apparatus includes a control circuit coupled to the switching circuit. The control circuit is operable to establish electrical coupling between a selected testing unit and one or more of the testing pads by selectively activating a subset of the switching devices.

FIELD OF THE INVENTION

The invention is directed to semiconductor fabrication, and in particular, to a method and apparatus of testing semiconductor devices.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs.

The fabrication of semiconductor devices may involve one or more testing processes. A plurality of test units and test pads may be used to carry out the testing. For traditional testing methods, the available number of test units is constrained by the available number of test pads. As semiconductor device continue to shrink, available space on a wafer becomes a valuable resource. As a result, the number of test pads on the wafer may be limited (e.g., less than 30) due to chip area consumption concerns, and that in turn limits the number of test units that can be implemented. As IC technologies continue to advance, the limited number of test units and test pads may not be sufficient to allow effective and efficient execution of the testing processes.

Therefore, while existing testing apparatuses and methodologies are generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1B are diagrammatic views of certain structures used for wafer testing.

FIG. 2 is a diagrammatic view of a testing apparatus according to various aspects of the present disclosure.

FIG. 3 is a diagrammatic view of a testing pad and a plurality of switching devices coupled thereto.

FIGS. 4A-4C are diagrammatic views of example switching devices.

FIGS. 5A-5B are diagrammatic views of example testing units.

FIG. 6 is a diagrammatic view of a control circuit, the testing pads, the testing units, and the switching devices.

FIG. 7 is a diagrammatic view of a testing apparatus that includes the control circuit, the testing pads, the testing units, and the switching devices.

FIG. 8 is a diagrammatic top view of the testing apparatus that includes the control circuit, the testing pads, the testing units, and the switching devices.

FIG. 9 is a flowchart illustrating a method for testing a wafer according to various aspects of the present disclosure.

BRIEF SUMMARY OF THE INVENTION

A semiconductor testing apparatus includes: a plurality of testing pads, a plurality of testing units, a switching circuit coupled between the testing pads and the testing units, and a control circuit coupled to the switching circuit. The switching circuit contains a plurality of switching devices. The control circuit is operable to establish electrical coupling between a selected testing unit and one or more of the testing pads by selectively activating a subset of the switching devices.

A device for testing a semiconductor wafer includes: a plurality of conductive test pads through which electrical signals can be applied, a plurality of test structures each containing a semiconductor circuit component, routing circuitry, and control circuitry. The routing circuitry contains a plurality of controllable switches that each include a control terminal and input/output terminals. Each switch is coupled between a respective one of the test pads and a respective one of the test structures through its input/output terminals. The control circuitry contains a plurality of storage elements driven by a clock signal. An output of each of the storage elements is coupled to a respective subset of the switches through their control terminals.

A method of testing a semiconductor device includes the following steps: providing a plurality of testing pads, providing a plurality of testing units, providing a plurality of controllable switching devices that are each coupled between a respective one of the testing pads and a respective one of the testing units, selectively activating a subset of the switching devices that are all coupled between a selected one of the testing units and at least a subset of the testing pads, wherein the selectively activating establishes electrical coupling between the selected testing unit and the subset of the testing pads.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Various features may be arbitrarily drawn in different scales for simplicity and clarity.

FIGS. 1A and 1B are circuit diagrammatic views of two example testing apparatuses for testing a semiconductor wafer. FIG. 1A illustrates a testing apparatus 40, which includes a plurality of testing units 50 whose various terminals are each coupled to a respective one of a plurality of testing pads 60. The testing units 50 are designed and implemented for the electrical testing of a semiconductor circuit element or component, such as a transistor or a resistor. Thus, the testing units 50 may each contain one of the semiconductor elements or components. The testing pads 60 are conductive pads for establishing electrical connections between the terminals of the testing units 50 and external devices. Electrical currents or voltages may be applied to the testing pads 60.

FIG. 1B illustrates a testing apparatus 70, which includes a plurality of testing units 80 and a plurality of testing pads 90. The testing units 80 and the testing pads 90 are coupled together by a decoder 95. The decoder 95 may contain a multiplexer, inverters, and/or Boolean logic gates such as AND, OR, NAND, NOR, XOR gates. The decoder 95 is operable to establish electrical connections between one or more of the testing units 80 and the testing pads 90.

A limitation of the testing apparatus 40 of FIG. 1A and the testing apparatus 70 of FIG. 1B is that they require too many testing pads 60. For instance, for the testing apparatus 40, twenty-one testing pads are used to effectively test eight testing units. Testing pads consume area on the wafer, which has become an increasingly valuable resource as the chip scaling down process continues. Therefore, having an excessive number of testing pads wastes resources. The testing apparatus 70 requires fewer testing pads than the testing apparatus 40. In general, the testing apparatus 70 can support X number of testing units with Y number of testing pads, where X=2^Y. However, this means that as the number of testing units increase, the number of testing pads still increases, even if the increase is not in a linear manner. Modern semiconductor fabrication may require an ever larger number of testing units to effectively test the performance of the wafer. Thus, the testing apparatus 70 may not be able to handle the demands of modern semiconductor fabrication, because it may not be able to supply enough testing pads (to support the number of the testing units required by modern semiconductor fabrication).

To address these shortcomings discussed above, the present disclosure implements a testing apparatus that utilizes a control circuit and a switching circuit to select desired testing units. Referring to FIG. 2, a simplified block diagram of a testing apparatus 100 is illustrated. The testing apparatus includes a plurality of testing pads represented by block 110, a plurality of testing units (also referred to as test structures) represented by block 120, a switching circuit/circuitry 130 (also referred to as routing circuit/circuitry), and a control circuit/circuitry 140.

The testing pads 110 include a plurality of conductive testing pads, through each of which a test signal can be applied. The test signal may be an electrical current or an electrical voltage. The testing units 120 include a plurality of test units that are designed and implemented for the testing of semiconductor circuit elements or components. For example, a testing unit may include an active device such as a transistor (e.g., field-effect transistor FET or bipolar junction transistor BJT) or a passive device such as a resistor, capacitor, or inductor. Each of the testing units 120 includes one or more terminals for electrically coupling with other devices.

The testing pads 110 and the testing units 120 are coupled together by the switching circuit 130. The switching circuit 130 contains a plurality of switching devices that can be selectively activated and deactivated (turned on and off, or closed and opened). The switching devices are each coupled to a respective one of the terminals of the testing units. The operation of the switching circuit 130 is electrically coupled to and controlled by the control circuit 140. The control circuit 140 includes devices that can selectively activate the switching devices. In an embodiment, the control circuit 140 includes a plurality of flip-flop devices as the control devices. The testing pads 110, the testing units 120, the switching circuit 130, and the control circuit 140 are discussed below in more detail.

FIG. 3 illustrates a simplified circuit diagrammatic view of a testing pad 110 and a plurality of switching devices 200 coupled thereto. The testing pad 110 includes a conductive material, for example copper or aluminum. An electrical signal (for example, a test signal) can be applied to the testing apparatus disclosed herein through the testing pad 110. A commonly used testing WAT testing pad size is 50 microns (um)×50 um in a 60 um height scribe line, pad pitch 100 um and pad space 50 um; in general, pad number in a WAT test line is more than 20. It is understood that alternative sizes and dimensions of the testing pads and scribe lines may be employed for various optimization considerations.

As is illustrated, the testing pad 110 is coupled to a plurality of switching devices 200. The switching devices 200 are switching devices of the switching circuit 130 of FIG. 2. Each switching device can be selectively activated to let an electrical signal pass through, or deactivated to let no electrical signal pass through. Although not illustrated for the sake of simplicity, it is understood that the testing apparatus of the present disclosure includes a plurality of additional testing pads similar to the testing pad 110, wherein these testing pads are each coupled to a plurality of switching devices similar to the switching devices 200 of FIG. 3.

FIGS. 4A-4B illustrate simplified circuit diagrams of different embodiments of the switching devices 200 of FIG. 3. In FIG. 4A, a switching device 200A includes a transmission gate. The transmission gate is implemented with a parallel combination of an NMOS transistor and a PMOS transistor. The signal at the gate of the NMOS transistor is complementary to the input at the gate of the PMOS transistor, or vice versa. For example, if a logical high (1) is applied at the gate of the NMOS transistor, then a logical low (0) is applied at the gate of the PMOS transistor.

The switching device 200A has input/output terminals 201-202 and control terminals 203-204. A data signal can be sent through the input/output terminals 201-202 and pass through the switching device 200A with negligible signal loss. A control signal can be applied to the control terminals 203-204. The control signal determines whether the switching device 200A is activated (turned on) or deactivated (off). In this manner, the switching device 200A serves as a bidirectional tunable switch—data signal can travel from the terminal 201 to the terminal 202 or from the terminal 202 to the terminal 201.

In FIG. 4B, a switching device 200B includes a PMOS pass gate. The PMOS pass gate is implemented using a PMOS transistor device. Similar to the transmission gate in FIG. 4A, the PMOS pass gate has input/output terminals 211-212 through which a data signal can be applied, and a control terminal 213 through which a control signal can be applied to activate or deactivate the PMOS pass gate. In FIG. 4C, a switching device 200C includes an NMOS pass gate. The NMOS pass gate is implemented using an NMOS transistor device. Similar to the transmission gate in FIG. 4A, the NMOS pass gate has input/output terminals 221-222 through which a data signal can be applied, and a control terminal 223 through which a control signal can be applied to activate or deactivate the NMOS pass gate. It is understood that the switching devices 200A-200C shown in FIGS. 4A-4C are merely examples, and that other suitable switching devices may be employed in alternative embodiments.

FIGS. 5A-5B include simplified circuit diagrams of example testing units that are embodiments of the testing units 120 shown in FIG. 2. In FIG. 5A, a testing unit 120A contains a transistor device, for example a FET transistor device. The transistor device has a gate terminal, a source terminal, a drain terminal, and a body terminal. Each of these terminals is coupled to two switching devices 200 (where the switching devices 200 may be implemented according to one of the embodiments shown in FIGS. 4A-4C or another suitable implementation). For each terminal of the transistor device, one of the switching devices 200 is used to force a signal (for example, an electrical current) to the terminal, and the other one of the switching devices 200 is used to sense a signal (for example, an electrical voltage) at the terminal. This type of forcing-sensing scheme can be used to compensate for circuit parasitics such as parasitic resistance.

In FIG. 5B, a testing unit 120B contains a resistor device. The resistor device has two terminals, each one of which is also coupled to two switching devices 200. Similar to the case in the testing unit 120A, one of the switching devices 200 can be used to force a current to a terminal of the testing unit 120B, while the other one of the switches 200 can be used to sense a voltage at that terminal. Each of the switches 200 of the testing units 120A and 120B is coupled to a respective one of the testing pads 110 shown in FIGS. 2-3.

It is understood that the testing units of the testing apparatus disclosed herein may have different implementations or configurations than what has been illustrated. For example, some testing units may only have a subset of their terminals coupled to switching devices, while the other terminals are left open or are grounded. As another example, some testing units may only have one or more terminals that are each coupled to one switching device instead of to two switching devices. For the sake of simplicity, these additional testing units are not illustrated herein.

FIG. 6 illustrates a simplified fragmentary circuit diagram of an embodiment of the control circuit 140 of FIG. 2. The control circuit 140 contains a plurality of storage elements, some of which are illustrated herein as storage elements 300-304. The storage elements 300-304 can store a state, such as a logical high (1) state or a logical low (0) state. In the embodiment shown, the storage elements 300-304 are implemented with D (data) flip-flop devices. Therefore, the storage elements 300-304 may also be referred to as flip-flop devices hereinafter. These flip-flop devices each have a D (data) input, a CLK (clock) input, an R (reset) input, a Q output, and a QB output (opposite of the Q output).

The flip-flop devices 300-304 are coupled together in series. The flip-flop device 300 has its D input coupled to a signal source 320, which outputs a logic high signal (1) in the present embodiment. For example, the signal source 320 may be tied to a power-rail such as Vdd or Vss. The QB output of the flip-flop device 300 is coupled to the D input of the flip-flop device 301, but for the rest of the flip-flop devices 301-304, each preceding flip-flop device has its Q output coupled to the D input of the subsequent flip-flop device. As an example, the flip-flop device 301 (the preceding flip-flop device in this example) has its Q output coupled to the D input of the flip-flop device 302 (the subsequent flip-flop device in this example).

The flip-flop devices 300-304 also each have their R input coupled to a reset signal 330. When the reset signal 330 is actuated, all the flip-flop devices 300-304 are reset. The flip-flop devices 300-304 also each have their CLK input coupled to a clock signal 340. A plurality of buffers 350-353 are used to buffer the clock signal 340 before the clock signal is received by the CLK input of the flip-flop devices 300-303.

The Q outputs of flip-flop devices 301-304 are coupled to switching devices 200A-200D, respectively. The switching devices 200A-200D are respectively coupled between testing units 120A-120D and a subset of testing pads 110. In other words, the testing units 120A-120D “share” the subset of testing pads 110, but not at the same time. Electrical connections may be established between the subset of the testing pads 110 and a particular one of the testing units 120A-120D if the switching devices for that testing unit are activated.

For example, electrical connections may be established between the testing pads 110 and the testing unit 120A if the switching devices 200A are activated (turned on) while the switching devices 200B-200D are deactivated (turned off). Meanwhile, since the switching devices 200B-200D are deactivated, no electrical connections are established between the testing units 120B-120D and the testing pads 110. It is understood that if the switching devices are transmission gates, an inverter may also be coupled to the Q output of the respective flip-flop device, so that logically-complementary control signals may be provided to the transmission gates from that flip-flop device.

The flip-flop devices 301-304 disclosed herein are configured to turn on one set of switching devices at a time (according to clock pulses), so as to activate only one testing unit at any given time. Thus, electrical connections between that testing unit and at least a subset of testing pads is established, while no electrical connections exist between the rest of the testing units and that subset of testing pads.

In more detail, at each pulse of the clock signal 340, one of the flip-flop devices outputs a logical high control signal at its Q output. For example, the flip-flop device 301 outputs a logical high control signal at its Q output. This logical high control signal activates the switching devices 200A, which allows the testing unit 120A to be electrically coupled to the testing pads 110. Meanwhile, the other flip-flop devices 302-304 output a logical low during this clock pulse, which means that the switching devices 200B-200D are turned off. Consequently, testing units 120B-120D are not activated and have no electrical connections with the testing pads 110 at this time.

At the next clock pulse, the flip-flop device 302 outputs a logical high and activates the switching devices 200B. This allows electrical connections to be established between the testing unit 120B and the testing pads 110. Meanwhile, the flip-flop devices 301 and 303-304 output a logical low and deactivates the switching devices 200A and 200C-200D. Thus, no electrical connections exist between the testing pads 110 and the testing units 120A and 120C-120D.

In this manner, at each clock pulse, a different one of the testing units is activated (through the set of switching devices coupled thereto) and is allowed access to the testing pads 110. Electrical testing may be done to that testing unit at that time by applying testing signals through the testing pads. This configuration allows the number of testing pads to remain at a fixable low number, even as the number of testing units increases.

It is understood that a plurality of additional flip-flop devices (and the corresponding switching devices and testing units) exist between the flip-flop devices 303 and 304, but they are not illustrated herein for the sake of simplicity. It is also understood that in alternative embodiments, other suitable digital circuit devices may be used to implement the storage elements 300-304, for example SR (set-reset) flip-flops, JK flip-flops, or latches.

FIG. 7 is a fragmentary circuit diagrammatic view of the testing apparatus 100 of FIG. 2. The testing apparatus 100 includes the testing pads 110, the testing units 120, the switching circuit 130, and the control circuit 140. A subset of the testing pads 110 is shown. In an embodiment, the testing pads 110 include eight testing pads for coupling to the four terminals of a transistor device (two testing pads for each terminal, i.e., one testing pad for forcing a current, another testing pad for sensing a voltage), one testing pad for the application of the Vdd signal, one testing pad for the application of the Vss signal, one testing pad for the application of the clock signal, and one testing pad for the application of the reset signal. Thus, a total of twelve testing pads are used in that embodiment. It is understood that other number of testing pads may be employed in alternative embodiments.

For the sake of simplicity, only two of the testing units are shown in FIG. 7 as testing units 120A and 120B, which contain FET transistor devices. The four terminals (gate, source, drain, body/bulk) of each FET transistor device are each coupled to two the testing pads 110 through two respective switching devices. The switching circuit 130 contains a plurality of such switching devices, which may be implemented using transmission gates, PMOS pass gates, or NMOS pass gates, as discussed above. The operation (opening or closing) of the switching devices are controlled by the control circuit 140, which contains a plurality of storage elements such as D flip-flops.

As discussed above with reference to FIG. 6, at each clock pulse, a respective subset of the switching devices is activated so as to enable electrical coupling between one of the testing units (such as the testing unit 120A) and at least a subset of the testing pads 110. Thus, each testing unit may be tested using the same set of testing pads 110 without causing electrical shorting. Stated differently, a plurality of testing units may “share” a common set of testing pads, but in a time-divided manner. At any given point in time, only one testing unit has access to the testing pads 110.

FIG. 8 is a simplified diagrammatic top level view of the testing apparatus 100 (of FIG. 2). In an embodiment, the testing apparatus 100 is implemented in a scribe line region of a wafer. The scribe line region includes regions between rows or columns of IC devices. Wafer cutting may take place in the scribe line region. The testing apparatus 100 may also be referred to as a test line. The testing apparatus 100 includes a plurality of testing pads 110. In an embodiment, there are twelve testing pads: four testing pads for signals Vdd, Vss, CLOCK, and RESET, eight testing pads for the four terminals of a transistor device (two testing pads for each terminal). The testing apparatus 100 includes a plurality of testing units 120, for example hundreds or thousands or testing units. The testing pads 110 may have dimensions that are significantly larger than the dimensions of the testing units. The testing pads 110 and the testing units 120 may at least partially overlap.

The testing apparatus 100 also contains circuitry 400. The circuitry 400 includes the switching circuit 130 of FIG. 2, as well as the control circuit 140 of FIG. 2. The switching circuit 130 contains controllable switching devices coupled between the testing pads 110 and the testing units 120. As discussed above, the control circuit 140 contains storage elements such as flip-flop devices that can control the operation of the switching devices so as to control which testing unit can have electrical access to the testing pads 120. The dimensions of each testing pad may also be significantly larger than the individual switching devices and/or flip-flop devices.

Illustrate in FIG. 9 is a flowchart of a method 500 for testing a semiconductor device according to various aspects of the present disclosure. It is also understood additional processes may be provided before, during, and after the method 500 of FIG. 9, and that some other processes may only be briefly described herein.

Referring to FIG. 9, the method 500 begins with block 510 in which a plurality of testing pads is provided. The method 500 continues with block 520 in which a plurality of testing units is provided. The method 500 continues with block 530 in which a plurality of controllable switching devices is provided. The switching devices are each coupled between a respective one of the testing pads and a respective one of the testing units. The method 500 continues with block 540 in which a subset of the switching devices is selectively activated. The subset of the switching devices is all coupled between a selected one of the testing units and at least a subset of the testing pads. The execution of block 540 establishes electrical coupling between the selected testing unit and the subset of the testing pads.

The embodiments disclosed herein offer advantages over existing testing apparatuses, it being understood that other embodiments may offer different advantages, and that no particular advantage is required for all embodiments. One advantage is the reduction of the number of testing pads. This is because the testing pads can now be “shared” by all the testing units in a time-divided manner. Typically, the testing pads take up much more room in a test line than the testing units, the control circuit, or the switching circuit. In other words, the implementation of the switching circuit, the control circuit, and/or extra testing units may not consume much chip area. In comparison, the reduction in the number of testing pads (for example from at twenty-one testing pads down to twelve) results in significant savings in chip area consumption, which may lead to lower fabrication costs.

In addition, the embodiments disclosed herein can handle a greater number of testing units than existing test lines. As discussed above, existing test lines may require more and more testing pads as the number of testing units continue to increase, which is the trend of modern semiconductor fabrication. At some point, the traditional test line may run out of space and may not be able to handle the additional testing units. Here, the number of testing pads can stay below a relatively low number, regardless of the number of testing units. As such, the embodiments disclosed herein are more adapted to handle the demands of modern (and future) semiconductor fabrication through its capability of tolerating an increasing number of testing units.

Furthermore, the embodiments disclosed herein are easy to implement and may not require extra fabrication processes. The switching circuit and the control circuit can be easily integrated into existing fabrication process flow.

One of the broader forms of the present disclosure involves a semiconductor testing apparatus. The testing apparatus includes: a plurality of testing pads; a plurality of testing units; a switching circuit coupled between the testing pads and the testing units, the switching circuit containing a plurality of switching devices; and a control circuit coupled to the switching circuit, the control circuit being operable to establish electrical coupling between a selected testing unit and one or more of the testing pads by selectively activating a subset of the switching devices.

Another one of the broader forms of the present disclosure involves a device for testing a semiconductor wafer. The device includes: a plurality of conductive test pads through which electrical signals can be applied; a plurality of test structures each containing a semiconductor circuit component; routing circuitry containing a plurality of controllable switches that each include a control terminal and input/output terminals, wherein each switch is coupled between a respective one of the test pads and a respective one of the test structures through its input/output terminals; and control circuitry containing a plurality of storage elements driven by a clock signal, wherein an output of each of the storage elements is coupled to a respective subset of the switches through their control terminals.

Another one of the broader forms of the present disclosure involves a method for testing a semiconductor device. The method includes: providing a plurality of testing pads; providing a plurality of testing units; providing a plurality of controllable switching devices that are each coupled between a respective one of the testing pads and a respective one of the testing units; and selectively activating a subset of the switching devices that are all coupled between a selected one of the testing units and at least a subset of the testing pads, wherein the selectively activating establishes electrical coupling between the selected testing unit and the subset of the testing pads.

The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor testing apparatus, comprising: a first number of testing pads; a second number of testing units, wherein each testing unit is a respective semiconductor circuit element, and wherein the second number is greater than the first number; a switching circuit coupled between the testing pads and the testing units, the switching circuit containing a plurality of switching devices; and a control circuit coupled to the switching circuit, the control circuit containing a plurality of storage elements, the control circuit being operable to establish electrical coupling between a selected testing unit and one or more of the testing pads by selectively activating a subset of the switching devices in a manner such that the testing units are electrically isolated from one another and such that the testing units share access to at least a common set of the testing pads in a time-divided manner, wherein the storage elements are driven by a clock signal having a plurality of pulses, and wherein at each pulse of the clock signal, the control circuit activates a different one of the testing units to have sole access to the test pads through the respective switching devices coupled thereto.
 2. The testing apparatus of claim 1, wherein: the testing units each include a plurality of terminals; and each switching device in the subset is electrically coupled between a respective terminal of the selected testing unit and one of the testing pads.
 3. The testing apparatus of claim 1, wherein the storage elements include flip-flop devices electrically coupled in series, and wherein an output of each flip-flop device is coupled to a respective subset of the switching devices.
 4. The testing apparatus of claim 3, wherein: the switching devices each include at least two input/output terminals and at least one control terminal; the testing pads and the testing units are each coupled to one or more input/output terminals of the switching devices; and the flip-flop devices are each coupled to one or more control terminals of the switching devices.
 5. The testing apparatus of claim 3, wherein the flip-flop devices are D flip-flop devices.
 6. The testing apparatus of claim 1, wherein at least one of: the testing pads and the testing units are implemented in a scribe line region of a wafer.
 7. The testing apparatus of claim 1, wherein: the testing pads each contain a conductive material through which an electrical signal can be applied; and the testing units each contain a semiconductor circuit element.
 8. The testing apparatus of claim 1, wherein the switching devices each include one of: a transmission gate, an NMOS pass gate, and a PMOS pass gate.
 9. A device for testing a semiconductor wafer, comprising: a plurality of conductive test pads through which electrical signals can be applied; a plurality of test structures each consisting of a semiconductor circuit component, wherein the plurality of test structures exceed the plurality of conductive test pads and wherein the test structures are located in a scribe-line region of the semiconductor wafer; routing circuitry containing a plurality of controllable switches that each include a control terminal and input/output terminals, wherein each switch is coupled between a respective one of the test pads and a respective one of the test structures through its input/output terminals; and control circuitry containing a plurality of storage elements driven by a clock signal, wherein the storage elements are electrically coupled in series, wherein an output of each of the storage elements is coupled to both of the following: a respective subset of the switches through their control terminals; and an input of a subsequent one of the storage elements electrically coupled in series thereto; wherein the routing circuitry and the control circuitry are configured so as to allow different test structures to gain access to at least common subset of the plurality of conductive test pads at different time slots, respectively.
 10. The device of claim 9, wherein: the switches each include one of: a transmission gate and a pass gate; and the storage elements each include a flip-flop device.
 11. The device of claim 10, wherein the flip-flop device is a D flip-flop device.
 12. The device of claim 9, wherein the clock signal contains a plurality of clock pulses, and wherein the control circuitry activates a different subset of the switches at each clock pulse.
 13. The device of claim 12, wherein each subset of the switches is coupled between a respective selected test structure and at least a subset of the test pads in a manner such that an activation of the subset of the switches establishes electrical connections between the selected test structure and the subset of the test pads while disallowing electrical connections between the subset of the test pads and any other test structure.
 14. A method of testing a semiconductor device, comprising: providing a first number of testing pads; providing a second number of testing units, wherein each testing unit is a respective portion of a semiconductor integrated circuit (IC) chip but not the entire IC chip, wherein the second number exceeds the first number; providing a plurality of controllable switching devices that are each coupled between a respective one of the testing pads and a respective one of the testing units; and selectively activating a subset of the switching devices that are all coupled between a selected one of the testing units and at least a subset of the testing pads, wherein the selectively activating establishes electrical coupling between the selected testing unit and the subset of the testing pads, wherein the selectively activating is performed in a manner such that the plurality of testing units share access to the plurality of testing pads in a time-divided manner, and wherein the selectively activating includes simultaneously deactivating a remaining portion of the switches other than the subset of the switches, so that no electrical coupling exists between the subset of the testing pads and a remaining portion of the testing units other than the selected testing unit.
 15. The method of claim 14, further including: generating a clock signal having a plurality of pulses, wherein the selectively activating includes driving a control circuitry with the clock signal.
 16. The method of claim 15, wherein the control circuitry includes a plurality of storage elements, and wherein the driving the control circuitry includes driving a clock input of each of the storage elements with the clock signal.
 17. The method of claim 16, wherein the driving the control circuitry is carried out in a manner such that each clock pulse causes one of the storage elements to output a logical high control signal, and wherein the control signal activates the subset of the switching devices.
 18. The method of claim 16, wherein the storage elements each include a flip-flop.
 19. The method of claim 18, wherein the plurality of storage elements are electrically coupled in series.
 20. The method of claim 14, wherein the providing the testing pads, the providing the testing units, and the providing the controllable switching devices are carried out in a manner such that at the plurality of testing units are implemented in a scribe line region of a semiconductor wafer. 